I can't see the unifying logic behind them. The standard "DM-1 for each previous career" seems needlessly punitive to me, and the fact that there are no positive modifiers just doesn't make sense. Merchant captains and the IISS should jump at an applicant with prior naval experience, for example.

It does echo real life to a degree. The longer you stay with a given career the harder it can be to transition to a new one. Which is why I like Condotterie’s suggestion about modifying the penalty if the character has skill levels important to the new career.

The age limits attached to the military career fit the real world too. Not sure I’d allow a skill to offset those. Although a mercenary career would be a different story...